I'm going with Sing.
Jamie Foxx's got good vocal structure. What he lacks is range and volume to his voice. It's not a powerful, signature voice like a Luther, Marvin, Teddy P, Stevie, Ray, David Ruffin, or Harold Melvin.
He's also lacking a signature song to showcase his voice. All of the guys I mentioned has a song that shows you the fullest extend of their power and grace in their voice. Jamie's first album doesn't do that. It's a generic R&B album. To Du's credit, you take his voice out, and sub in any one of 15-25 current guys out there, and it would sound the same, or better.
Doesn't mean Jamie doesn't have talent; it's clear the talent is there. It's just with all the other things he can do, he never honed in on his vocal capabilities and overall singing potential, and you can hear that.